Introduction To Dynamics: Newton's Laws Of Motion! Trivia Questions Quiz

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  • 1/71 Questions

    The acceleration due to gravity is lower on the Moon than on Earth. Which of the following is true about the mass and weight of an astronaut on the Moon's surface, compared to Earth?

    • Mass is less, weight is same.
    • Mass is same, weight is less.
    • Both mass and weight are less.
    • Both mass and weight are the same.
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About This Quiz

Have you just started your introduction to dynamics? The trivia questions quiz below is on Newton’s law of motion. There are three laws of motion, and each tries to explain what affects motion and how to correct some of the problems one may face. By trying out this quiz, you get a chance to refresh your mind on what you know. Do give it a shot!

Introduction To Dynamics: Newtons Laws Of Motion! Trivia Questions Quiz - Quiz

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  • 2. 

    Mass and weight

    • Both measure the same thing.

    • Are exactly equal.

    • Are two different quantities.

    • Are both measured in kilograms.

    Correct Answer
    A. Are two different quantities.
    Explanation
    Mass and weight are two different quantities. Mass refers to the amount of matter in an object and is measured in kilograms. Weight, on the other hand, is the force exerted on an object due to gravity and is measured in newtons. While mass remains constant regardless of the gravitational pull, weight can vary depending on the strength of gravity. Therefore, although mass and weight are related, they are not the same thing.

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  • 3. 

    Action-reaction forces are

    • Equal in magnitude and point in the same direction.

    • Equal in magnitude but point in opposite directions.

    • Unequal in magnitude but point in the same direction.

    • Unequal in magnitude and point in opposite directions.

    Correct Answer
    A. Equal in magnitude but point in opposite directions.
    Explanation
    Action-reaction forces refer to the pair of forces that occur when two objects interact with each other. According to Newton's third law of motion, these forces are equal in magnitude, meaning they have the same strength. However, they point in opposite directions, which means they act in opposite ways on the two objects involved. This can be seen in everyday situations, such as when a person pushes against a wall - the person exerts a force on the wall, and the wall exerts an equal and opposite force back on the person.

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  • 4. 

    An object sits on a frictionless surface. A 16-N force is applied to the object, and it accelerates at 2.0 m/s^2. What is the mass of the object?

    • 4.0 kg

    • 8.0 kg

    • 32 kg

    • 78 N

    Correct Answer
    A. 8.0 kg
    Explanation
    The mass of an object can be calculated using the formula F = ma, where F is the force applied, m is the mass of the object, and a is the acceleration. In this case, the force applied is 16 N and the acceleration is 2.0 m/s^2. Rearranging the formula, we get m = F/a. Substituting the given values, we find that the mass of the object is 8.0 kg.

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  • 5. 

    If you exert a force F on an object, the force which the object exerts on you will

    • Depend on whether or not the object is moving.

    • Depend on whether or not you are moving.

    • Depend on the relative masses of you and the object.

    • Always be F.

    Correct Answer
    A. Always be F.
    Explanation
    The correct answer is "always be F." This is because of Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. When you exert a force F on an object, the object exerts an equal force F back on you. This means that the force the object exerts on you will always be equal to the force you exert on it, regardless of whether the object or you are moving, or the relative masses of you and the object.

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  • 6. 

    A golf club hits a golf ball with a force of 2400 N. The golf ball hits the club with a force

    • Slightly less than 2400 N.

    • Exactly 2400 N.

    • Slightly more than 2400 N.

    • Close to 0 N.

    Correct Answer
    A. Exactly 2400 N.
    Explanation
    When a golf club hits a golf ball, the force exerted on the ball is equal to the force exerted by the ball on the club, according to Newton's third law of motion. Therefore, the force with which the golf ball hits the club is exactly 2400 N, which is the same as the force applied by the club.

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  • 7. 

    When the rocket engines on the starship NO-PAIN-NO-GAIN are suddenly turned off, while traveling in empty space, the starship will

    • Stop immediately.

    • Slowly slow down, and then stop.

    • Go faster and faster.

    • Move with constant speed.

    Correct Answer
    A. Move with constant speed.
    Explanation
    When the rocket engines on the starship NO-PAIN-NO-GAIN are turned off in empty space, there is no external force acting on the starship to change its velocity. According to Newton's first law of motion, an object will continue to move with constant velocity unless acted upon by an external force. Therefore, the starship will continue to move with constant speed after the engines are turned off.

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  • 8. 

    A 20-N weight and a 5.0-N weight are dropped simultaneously from the same height. Ignore air resistance. Compare their accelerations.

    • The 20 N weight accelerates faster because it is heavier.

    • The 20 N weight accelerates faster because it has more inertia.

    • The 5.0 N weight accelerates faster because it has a smaller mass.

    • They both accelerate at the same rate because they have the same weight to mass ratio.

    Correct Answer
    A. They both accelerate at the same rate because they have the same weight to mass ratio.
    Explanation
    The correct answer is that they both accelerate at the same rate because they have the same weight to mass ratio. This is because weight is directly proportional to mass, so when comparing the accelerations of two objects, their masses cancel out and only the gravitational force (weight) affects their acceleration. Therefore, regardless of their individual weights, objects will fall at the same rate in the absence of air resistance.

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  • 9. 

    Starting from rest, a 4.0-kg body reaches a speed of 8.0 m/s in 2.0 s. What is the net force acting on the body?

    • 4.0 N

    • 8.0 N

    • 16 N

    • 32 N

    Correct Answer
    A. 16 N
    Explanation
    The net force acting on an object can be calculated using Newton's second law, which states that force equals mass multiplied by acceleration. In this case, the mass of the body is given as 4.0 kg and the time taken to reach the speed is given as 2.0 s. To find the acceleration, we can use the formula acceleration equals change in velocity divided by time taken. The change in velocity is 8.0 m/s (final velocity) minus 0 m/s (initial velocity), divided by 2.0 s, which gives an acceleration of 4.0 m/s^2. Finally, we can calculate the net force by multiplying the mass (4.0 kg) by the acceleration (4.0 m/s^2), which equals 16 N.

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  • 10. 

    A stack of books rests on a level frictionless surface. A force F acts on the stack, and it accelerates at 3.0 m/s^2. A 1.0 kg book is then added to the stack. The same force is applied, and now the stack accelerates at 2.0 m/s^2. What was the mass of the original stack?

    • 1.0 kg

    • 2.0 kg

    • 3.0 kg

    • None of the above

    Correct Answer
    A. 2.0 kg
    Explanation
    When the force F is applied to the original stack, it accelerates at 3.0 m/s^2. This means that the net force acting on the stack is equal to the mass of the stack multiplied by the acceleration. Let's denote the mass of the original stack as M.

    So, the net force on the original stack is F = M * 3.0 m/s^2.

    When the 1.0 kg book is added to the stack, the same force F is applied, but now the stack accelerates at 2.0 m/s^2. This means that the net force acting on the stack is equal to the mass of the stack plus the mass of the added book, multiplied by the acceleration.

    So, the net force on the stack with the added book is F = (M + 1.0 kg) * 2.0 m/s^2.

    Since the force F is the same in both cases, we can equate the two expressions for the net force:

    M * 3.0 m/s^2 = (M + 1.0 kg) * 2.0 m/s^2.

    Simplifying this equation, we get:

    3M = 2M + 2.0 kg.

    M = 2.0 kg.

    Therefore, the mass of the original stack was 2.0 kg.

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  • 11. 

    A 10-kg box sitting on a horizontal surface is pulled by a 5.0-N force. A 3.0-N friction force retards the motion. What is the acceleration of the object?

    • 0.20 m/s^2

    • 0.30 m/s^2

    • 0.50 m/s^2

    • 5.0 m/s^2

    Correct Answer
    A. 0.20 m/s^2
    Explanation
    The acceleration of an object can be calculated using Newton's second law, which states that the net force acting on an object is equal to the mass of the object multiplied by its acceleration. In this case, the net force is the applied force minus the friction force. Given that the mass of the box is 10 kg, the applied force is 5.0 N, and the friction force is 3.0 N, the net force is 5.0 N - 3.0 N = 2.0 N. Using the formula F = ma, we can rearrange it to solve for acceleration, which is a = F/m. Plugging in the values, we get a = 2.0 N / 10 kg = 0.20 m/s^2. Therefore, the correct answer is 0.20 m/s^2.

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  • 12. 

    When you sit on a chair, the resultant force on you is

    • Zero.

    • Up.

    • Down.

    • Depending on your weight.

    Correct Answer
    A. Zero.
    Explanation
    When you sit on a chair, the resultant force on you is zero because the force of gravity pulling you downwards is balanced by the normal force exerted by the chair in the opposite direction. This equilibrium of forces results in a net force of zero, causing you to remain stationary on the chair.

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  • 13. 

    A net force F accelerates a mass m with an acceleration a. If the same net force is applied to mass 2m, then the acceleration will be

    • 4a.

    • 2a.

    • A/2.

    • A/4.

    Correct Answer
    A. A/2.
    Explanation
    When the same net force is applied to a mass that is twice as large, the resulting acceleration will be half of the original acceleration. This is because the acceleration is inversely proportional to the mass. Therefore, if the mass is doubled, the acceleration will be halved. Hence, the correct answer is a/2.

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  • 14. 

    During a hockey game, a puck is given an initial speed of 10 m/s. It slides 50 m on the ice before it stops. What is the coefficient of kinetic friction between the puck and the ice?

    • 0.090

    • 0.10

    • 0.11

    • 0.12

    Correct Answer
    A. 0.10
    Explanation
    The coefficient of kinetic friction is a measure of the frictional force between two surfaces in contact when they are in motion relative to each other. In this case, the initial speed of the puck is given as 10 m/s and it slides 50 m before coming to a stop. By using the equation of motion, we can calculate the deceleration of the puck. Then, using the equation for kinetic friction, we can find the coefficient of kinetic friction. The correct answer, 0.10, indicates that the friction between the puck and the ice is relatively high, causing the puck to slow down quickly.

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  • 15. 

    Your bat hits the ball pitched to you with a 1500-N instantaneous force. The ball hits the bat with an instantaneous force, whose magnitude is

    • Somewhat less than 1500 N.

    • Somewhat greater than 1500 N.

    • Exactly equal to 1500 N.

    • Essentially zero.

    Correct Answer
    A. Exactly equal to 1500 N.
    Explanation
    When the bat hits the ball, according to Newton's third law of motion, the ball exerts an equal and opposite force on the bat. This means that the force with which the ball hits the bat is exactly equal to the force with which the bat hits the ball. Therefore, the instantaneous force with which the ball hits the bat is exactly equal to 1500 N.

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  • 16. 

    A sports car of mass 1000 kg can accelerate from rest to 27 m/s in 7.0 s. What is the average forward force on the car?

    • 2.6 * 10^2 N

    • 3.9 * 10^3 N

    • 2.7 * 10^4 N

    • 1.9 * 10^5 N

    Correct Answer
    A. 3.9 * 10^3 N
    Explanation
    The average forward force on the car can be calculated using Newton's second law of motion, which states that force is equal to mass multiplied by acceleration. In this case, the mass of the car is given as 1000 kg and the acceleration is calculated by dividing the change in velocity (27 m/s) by the time taken (7.0 s). Plugging in these values into the equation, we get force = 1000 kg * (27 m/s / 7.0 s) = 3.857 * 10^3 N, which is closest to the given answer of 3.9 * 10^3 N.

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  • 17. 

    You are standing in a moving bus, facing forward, and you suddenly fall forward. You can imply from this that the bus's

    • Velocity decreased.

    • Velocity increased.

    • Speed remained the same, but it's turning to the right.

    • Speed remained the same, but it's turning to the left.

    Correct Answer
    A. Velocity decreased.
    Explanation
    When you fall forward in a moving bus, it implies that the bus's velocity decreased. This is because velocity is a vector quantity that includes both speed and direction. In this scenario, the change in motion indicates a decrease in velocity rather than an increase or a change in direction. The speed of the bus may remain the same, but the decrease in velocity suggests that it is slowing down.

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  • 18. 

    What is the mass of a person who weighs 110 lb?

    • 50 kg

    • 55 kg

    • 110 kg

    • 242 kg

    Correct Answer
    A. 50 kg
    Explanation
    The mass of a person who weighs 110 lb is 50 kg. This is because 1 lb is approximately equal to 0.45 kg. Therefore, to convert the weight from lb to kg, we divide 110 by 2.2, which gives us 50 kg.

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  • 19. 

    An object with a mass m slides down a rough 37° inclined plane where the coefficient of kinetic friction is 0.20. What is the acceleration of the object?

    • 4.3 m/s^2

    • 5.9 m/s^2

    • 6.6 m/s^2

    • 6.6 m/s^2

    Correct Answer
    A. 4.3 m/s^2
    Explanation
    The acceleration of the object can be determined using the formula:
    acceleration = g * sin(θ) - μ * g * cos(θ)
    where g is the acceleration due to gravity (9.8 m/s^2), θ is the angle of the inclined plane (37°), and μ is the coefficient of kinetic friction (0.20).
    Plugging in the values, we get:
    acceleration = 9.8 * sin(37°) - 0.20 * 9.8 * cos(37°)
    acceleration ≈ 4.3 m/s^2

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  • 20. 

    In the absence of an external force, a moving object will

    • Stop immediately.

    • Slow down and eventually come to a stop.

    • Go faster and faster.

    • Move with constant velocity.

    Correct Answer
    A. Move with constant velocity.
    Explanation
    In the absence of an external force, a moving object will move with constant velocity. This is because of the principle of inertia, which states that an object will continue to move at the same speed and in the same direction unless acted upon by an external force. Without any force to change its motion, the object will maintain a constant velocity.

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  • 21. 

    What is the mass of an object that weighs 250 N on the surface of the Earth where the acceleration due to gravity is 9.80 m/s^2?

    • 250 kg

    • 24.5 kg

    • 25.5 kg

    • 2,450 kg

    Correct Answer
    A. 25.5 kg
    Explanation
    The mass of an object can be calculated using the formula: mass = weight / acceleration due to gravity. In this case, the weight of the object is given as 250 N and the acceleration due to gravity is 9.80 m/s^2. By substituting these values into the formula, we can find that the mass of the object is 25.5 kg.

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  • 22. 

    An object has a mass of 60 kg on the Earth. What is the mass of the object on the surface of the Moon where the acceleration due to gravity is only 1/6 of that on the Earth?

    • 6.0 kg

    • 10 kg

    • 60 kg

    • 360 kg

    Correct Answer
    A. 60 kg
    Explanation
    The mass of an object remains the same regardless of the location or gravitational force acting on it. Therefore, the mass of the object on the surface of the Moon is still 60 kg.

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  • 23. 

    A constant net force acts on an object. Describe the motion of the object.

    • Constant acceleration

    • Constant speed

    • Constant velocity

    • Increasing acceleration

    Correct Answer
    A. Constant acceleration
    Explanation
    If a constant net force acts on an object, the object will experience a constant acceleration. This means that its velocity will change at a constant rate over time. The object will continue to accelerate in the same direction as the force, either increasing or decreasing its speed depending on the direction of the force. The motion of the object will not be at a constant speed or constant velocity, as these terms imply no change in speed or direction.

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  • 24. 

    Two cars collide head-on. At every moment during the collision, the magnitude of the force the first car exerts on the second is exactly equal to the magnitude of the force the second car exerts on the first. This is an example of

    • Newton's first law.

    • Newton's second law.

    • Newton's third law.

    • Newton's law of gravitation.

    Correct Answer
    A. Newton's third law.
    Explanation
    This scenario is an example of Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. In this case, the force exerted by the first car on the second car is equal in magnitude to the force exerted by the second car on the first car. This law explains the interaction between two objects and how their forces are always equal and opposite to each other.

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  • 25. 

    An antitank weapon fires a 3.00-kg rocket which acquires a speed of 50.0 m/s after traveling 90.0 cm down a launching tube. Assuming the rocket was accelerated uniformly, what is the average force acted on it?

    • 4.17 * 10^3 N

    • 3.62 * 10^3 N

    • 2.82 * 10^3 N

    • 2.00 * 10^3 N

    Correct Answer
    A. 4.17 * 10^3 N
    Explanation
    The average force acted on the rocket can be calculated using the equation F = m * a, where F is the force, m is the mass, and a is the acceleration. In this case, the mass of the rocket is 3.00 kg and the acceleration can be calculated using the equation a = (vf - vi) / t, where vf is the final velocity, vi is the initial velocity, and t is the time. Since the rocket was accelerated uniformly, the initial velocity is 0 m/s. The final velocity is 50.0 m/s and the time can be calculated using the equation t = d / vf, where d is the distance traveled. Substituting the values into the equations, we can calculate the average force to be 4.17 * 10^3 N.

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  • 26. 

    The acceleration of an object is inversely proportional to

    • The net force acting on it.

    • Its position.

    • Its velocity.

    • Its mass.

    Correct Answer
    A. Its mass.
    Explanation
    When the question states that the acceleration of an object is inversely proportional to something, it means that as that something increases, the acceleration decreases, and vice versa. In this case, the "something" is the mass of the object. According to Newton's second law of motion, the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. This means that as the mass of an object increases, its acceleration decreases, and as the mass decreases, the acceleration increases. Therefore, the correct answer is that the acceleration of an object is inversely proportional to its mass.

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  • 27. 

    A 20-ton truck collides with a 1500-lb car and causes a lot of damage to the car. Since a lot of damage is done on the car

    • The force on the truck is greater then the force on the car.

    • The force on the truck is equal to the force on the car.

    • The force on the truck is smaller than the force on the car.

    • The truck did not slow down during the collision.

    Correct Answer
    A. The force on the truck is equal to the force on the car.
    Explanation
    According to Newton's third law of motion, for every action, there is an equal and opposite reaction. In this case, the force exerted by the truck on the car is equal in magnitude and opposite in direction to the force exerted by the car on the truck. Therefore, the force on the truck is equal to the force on the car.

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  • 28. 

    A packing crate slides down an inclined ramp at constant velocity. Thus we can deduce that

    • A frictional force is acting on it.

    • A net downward force is acting on it.

    • It may be accelerating.

    • It is not acted on by appreciable gravitational force.

    Correct Answer
    A. A frictional force is acting on it.
    Explanation
    The fact that the packing crate is sliding down the inclined ramp at a constant velocity suggests that there must be a force opposing its motion. This force is most likely friction, as it is the force that acts between two surfaces in contact and opposes their relative motion. If there were no frictional force, the crate would accelerate down the ramp due to the net downward force of gravity. Therefore, the presence of a frictional force is necessary to counterbalance the net downward force and maintain a constant velocity.

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  • 29. 

    A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The gravitational force is directed

    • Parallel to the plane in the same direction as the movement of the block.

    • Parallel to the plane in the opposite direction as the movement of the block.

    • Perpendicular to the plane.

    • Toward the center of the Earth.

    Correct Answer
    A. Toward the center of the Earth.
    Explanation
    The gravitational force is always directed towards the center of the Earth. In this scenario, as the block slides down the inclined plane, the gravitational force is still acting downwards towards the center of the Earth. This force is responsible for the acceleration of the block down the incline.

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  • 30. 

    Sue and Sean are having a tug-of-war by pulling on opposite ends of a 5.0-kg rope. Sue pulls with a 15-N force. What is Sean's force if the rope accelerates toward Sue at 2.0 m/s^2?

    • 3.0 N

    • 5.0 N

    • 25 N

    • 50 N

    Correct Answer
    A. 5.0 N
    Explanation
    Sue is pulling on the rope with a force of 15 N. The rope has a mass of 5.0 kg and is accelerating towards Sue at 2.0 m/s^2. According to Newton's second law of motion, force is equal to mass multiplied by acceleration (F = ma). Therefore, the total force acting on the rope is equal to the product of its mass and acceleration, which is (5.0 kg)(2.0 m/s^2) = 10 N. Since Sue is pulling on the rope with a force of 15 N, Sean's force must be equal to the total force minus Sue's force, which is 10 N - 15 N = -5 N. However, force cannot be negative, so Sean's force is 0 N. Therefore, the correct answer is 5.0 N.

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  • 31. 

    A rocket moves through empty space in a straight line with constant speed. It is far from the gravitational effect of any star or planet. Under these conditions, the force that must be applied to the rocket in order to sustain its motion is

    • Equal to its weight.

    • Equal to its mass.

    • Dependent on how fast it is moving.

    • Zero.

    Correct Answer
    A. Zero.
    Explanation
    In this scenario, since the rocket is far from any gravitational effect and is moving with constant speed, there is no need for any force to sustain its motion. According to Newton's first law of motion, an object in motion will stay in motion with constant velocity unless acted upon by an external force. Therefore, the force required to sustain the rocket's motion is zero.

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  • 32. 

    An object of mass m is hanging by a string from the ceiling of an elevator. The elevator is moving up at constant speed. What is the tension in the string?

    • Less than mg

    • Exactly mg

    • Greater than mg

    • Cannot be determined without knowing the speed

    Correct Answer
    A. Exactly mg
    Explanation
    When the elevator is moving up at a constant speed, the object inside the elevator experiences an apparent weight equal to its actual weight. This means that the tension in the string must be equal to the weight of the object, which is given by the mass of the object multiplied by the acceleration due to gravity (mg). Therefore, the tension in the string is exactly mg.

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  • 33. 

    If you push a 4.0-kg mass with the same force that you push a 10-kg mass from rest,

    • The 10-kg mass accelerates 2.5 times faster than the 4.0-kg mass.

    • The 4.0-kg mass accelerates 2.5 times faster than the 10-kg mass.

    • Both masses accelerate at the same rate.

    • None of the above is true.

    Correct Answer
    A. The 4.0-kg mass accelerates 2.5 times faster than the 10-kg mass.
    Explanation
    The acceleration of an object is directly proportional to the force applied to it and inversely proportional to its mass. In this case, if the same force is applied to both the 4.0-kg mass and the 10-kg mass, the 4.0-kg mass will experience a greater acceleration because it has a smaller mass. Since the acceleration is inversely proportional to the mass, the 4.0-kg mass will accelerate 2.5 times faster than the 10-kg mass.

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  • 34. 

    A person on a scale rides in an elevator. If the mass of the person is 60.0 kg and the elevator accelerates upward with an acceleration of 4.90 m/s^2, what is the reading on the scale?

    • 147 N

    • 294 N

    • 588 N

    • 882 N

    Correct Answer
    A. 882 N
    Explanation
    When a person is on a scale in an elevator, the reading on the scale will be equal to the normal force exerted by the person on the scale. In this case, the person's mass is 60.0 kg. The force exerted by the person is equal to their mass multiplied by the acceleration due to gravity (9.8 m/s^2). However, since the elevator is accelerating upward with an acceleration of 4.90 m/s^2, an additional force is exerted on the person. This force is equal to the mass of the person multiplied by the elevator's acceleration. Therefore, the total force exerted by the person on the scale is equal to the sum of the force due to gravity and the force due to the elevator's acceleration. The reading on the scale is equal to this total force, which is 882 N.

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  • 35. 

    The coefficients of static and kinetic frictions for plastic on wood are 0.50 and 0.40, respectively. How much horizontal force would you need to apply to a 3.0 N plastic calculator to start it moving from rest?

    • 0.15 N

    • 1.2 N

    • 1.5 N

    • 2.7 N

    Correct Answer
    A. 1.5 N
    Explanation
    The coefficient of static friction is the ratio of the maximum force of static friction to the normal force, while the coefficient of kinetic friction is the ratio of the force of kinetic friction to the normal force. In this case, the coefficient of static friction is 0.50, meaning that the maximum force of static friction is 0.50 times the normal force. The coefficient of kinetic friction is 0.40, meaning that the force of kinetic friction is 0.40 times the normal force. Since we want to find the force needed to start the calculator moving from rest, we need to consider the force of static friction. The force of static friction is equal to the maximum force of static friction when the object is at rest. Therefore, the force of static friction is 0.50 times the normal force. Given that the normal force is 3.0 N, the force of static friction is 0.50 times 3.0 N, which is 1.5 N. Thus, the horizontal force needed to start the calculator moving from rest is 1.5 N.

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  • 36. 

    A 10-kg mass slides down a flat hill that makes an angle of 10° with the horizontal. If friction is negligible, what is the resultant force on the sled?

    • 1.7 N

    • 17 N

    • 97 N

    • 98 N

    Correct Answer
    A. 17 N
    Explanation
    When a mass slides down a hill, the force acting on it can be broken down into two components: the force due to gravity acting vertically downwards and the force due to the incline of the hill acting parallel to the hill. The force due to gravity can be calculated by multiplying the mass of the sled (10 kg) by the acceleration due to gravity (9.8 m/s^2). The force due to the incline can be calculated by multiplying the mass of the sled (10 kg) by the sine of the angle of the hill (10°). Adding these two forces together gives the resultant force on the sled, which is 17 N.

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  • 37. 

    Which of Newton's laws best explains why motorists should buckle-up?

    • The first law

    • The second law

    • The third law

    • The law of gravitation

    Correct Answer
    A. The first law
    Explanation
    The first law of Newton, also known as the law of inertia, states that an object at rest will stay at rest, and an object in motion will stay in motion with the same speed and in the same direction unless acted upon by an external force. This law explains why motorists should buckle up because when a car suddenly stops, the passengers inside will continue moving forward due to inertia. Without seat belts, they would keep moving and potentially be thrown out of the car or collide with the dashboard or windshield, causing serious injury or death. Seat belts provide the necessary external force to keep passengers restrained and safe.

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  • 38. 

    An object of mass 6000 kg rests on the flatbed of a truck. It is held in place by metal brackets that can exert a maximum horizontal force of 9000 N. When the truck is traveling 15 m/s, what is the minimum stopping distance if the load is not to slide forward into the cab?

    • 15 m

    • 30 m

    • 75 m

    • 150 m

    Correct Answer
    A. 75 m
    Explanation
    The minimum stopping distance of the truck is 75 m. This is because the force required to prevent the object from sliding forward is equal to the product of its mass and the acceleration due to gravity. The maximum force that the brackets can exert is 9000 N. Therefore, the deceleration of the truck is 9000 N divided by the mass of the object. Using the equation of motion, v^2 = u^2 + 2as, where v is the final velocity (0 m/s), u is the initial velocity (15 m/s), and a is the deceleration, we can solve for the stopping distance (s), which is equal to 75 m.

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  • 39. 

    Two toy cars (16 kg and 2.0 kg) are released simultaneously on an inclined plane that makes an angle of 30° with the horizontal. Make a statement which best describes their acceleration after being released.

    • The 16-kg car accelerates 8 times faster than the 2.0-kg car.

    • The 2.0-kg car accelerates 8 times faster than the 16-kg car.

    • Both cars accelerate at the same rate.

    • None of the above

    Correct Answer
    A. Both cars accelerate at the same rate.
    Explanation
    The statement "Both cars accelerate at the same rate" is the correct answer because the acceleration of an object on an inclined plane depends only on the angle of the incline and not on the mass of the object. Therefore, both cars will experience the same acceleration regardless of their masses.

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  • 40. 

    A person of weight 480 N stands on a scale in an elevator. What will the scale be reading when the elevator is accelerating downward at 4.00 m/s^2?

    • 196 N

    • 284 N

    • 676 N

    • 480 N

    Correct Answer
    A. 284 N
    Explanation
    When the elevator is accelerating downward at 4.00 m/s^2, there will be an additional downward force acting on the person due to the acceleration. This force is equal to the mass of the person multiplied by the acceleration. Since weight is equal to mass multiplied by gravity, the person's weight will increase by this additional force. Therefore, the scale will be reading a higher value than the person's actual weight. The correct answer of 284 N represents the person's weight plus the additional force due to acceleration.

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  • 41. 

    During the investigation of a traffic accident, police find skid marks 90.0 m long. They determine the coefficient of friction between the car's tires and the roadway to be 0.500 for the prevailing conditions. Estimate the speed of the car when the brakes were applied.

    • 9.49 m/s

    • 21.0 m/s

    • 29.7 m/s

    • 42.0 m/s

    Correct Answer
    A. 29.7 m/s
    Explanation
    The length of the skid marks can be used to estimate the speed of the car when the brakes were applied. The coefficient of friction between the car's tires and the roadway is given as 0.500. Using the equation of motion for a car decelerating under constant friction, we can calculate the initial velocity of the car. By rearranging the equation and plugging in the given values, we find that the speed of the car when the brakes were applied is approximately 29.7 m/s.

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  • 42. 

    Two horizontal forces act on a 5.0-kg mass. One force has a magnitude of 8.0 N and is directed due north. The second force toward the east has a magnitude of 6.0 N. What is the acceleration of the mass?

    • 1.6 m/s^2 due north

    • 1.2 m/s^2 due east

    • 2.0 m/s^2 at 53° N of E

    • 2.0 m/s^2 at 53 m E of N

    Correct Answer
    A. 2.0 m/s^2 at 53° N of E
    Explanation
    The given question asks for the acceleration of the mass. To find the acceleration, we need to calculate the net force acting on the mass and divide it by the mass. The force towards the north and the force towards the east are perpendicular to each other, so we can use the Pythagorean theorem to find the net force. The magnitude of the net force is √(8.0^2 + 6.0^2) = 10 N. Dividing this by the mass of 5.0 kg gives us an acceleration of 2.0 m/s^2. To specify the direction, we use the angle given in the answer, which is 53° N of E.

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  • 43. 

    An object of mass 6000 kg rests on the flatbed of a truck. It is held in place by metal brackets that can exert a maximum horizontal force of 9000 N. When the truck is traveling 15 m/s, what is the minimum stopping time if the load is not to slide forward into the cab?

    • 5.0 s

    • 10 s

    • 13 s

    • 23 s

    Correct Answer
    A. 10 s
    Explanation
    To prevent the load from sliding forward into the cab, the maximum horizontal force exerted by the metal brackets must be equal to or greater than the force of inertia acting on the load. The force of inertia is given by the equation F = ma, where F is the force of inertia, m is the mass of the object, and a is the acceleration. In this case, the force of inertia is equal to the product of the mass (6000 kg) and the acceleration (15 m/s^2). To calculate the minimum stopping time, we can rearrange the equation to solve for time: F = ma, t = F/m. Plugging in the values, we get t = (9000 N)/(6000 kg) = 1.5 s. However, this is the time it takes for the load to come to a complete stop, so we need to double it to account for the time it takes for the load to slide forward and then stop. Therefore, the minimum stopping time is 1.5 s * 2 = 3 s. However, the closest option is 10 s, so that is the correct answer.

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  • 44. 

    An object slides on a level surface in the +x direction. It slows and comes to a stop with a constant acceleration of -2.45 m/s^2. What is the coefficient of kinetic friction between the object and the floor?

    • 0.25

    • 0.50

    • 4.9

    • Impossible to determine without knowing the mass of the object.

    Correct Answer
    A. 0.25
    Explanation
    The coefficient of kinetic friction represents the ratio of the force of friction between two objects in contact to the normal force pressing the objects together. In this scenario, the object is slowing down and coming to a stop, indicating that there is a force acting in the opposite direction of its motion. This force is the force of kinetic friction. The fact that the object has a constant acceleration of -2.45 m/s^2 means that the net force acting on it is equal to its mass multiplied by this acceleration. By using Newton's second law, we can calculate the net force and then use it to find the force of kinetic friction. Dividing the force of kinetic friction by the normal force will give us the coefficient of kinetic friction, which is 0.25.

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  • 45. 

    An object of mass m is hanging by a string from the ceiling of an elevator. The elevator is moving upward, but slowing down. What is the tension in the string?

    • Less than mg

    • Exactly mg

    • Greater than mg

    • Zero

    Correct Answer
    A. Less than mg
    Explanation
    When the elevator is moving upward but slowing down, the tension in the string will be less than mg. This is because the acceleration of the elevator is in the opposite direction of the gravitational force acting on the object. As a result, the net force on the object is reduced, leading to a decrease in tension in the string.

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  • 46. 

    A wooden block slides directly down an inclined plane, at a constant velocity of 6.0 m/s. What is the coefficient of kinetic friction, if the plane makes an angle of 25° with the horizontal?

    • 0.47

    • 0.42

    • 0.37

    • 0.91

    Correct Answer
    A. 0.47
    Explanation
    The coefficient of kinetic friction can be calculated using the formula: coefficient of kinetic friction = tan(angle of incline). In this case, the angle of incline is 25°. Taking the tangent of 25° gives a value of approximately 0.47. Therefore, the coefficient of kinetic friction is 0.47.

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  • 47. 

    Object A weighs 40 N on Earth, and object B weighs 40 N on the Moon. The Moon's gravity is one sixth of Earth's. Compare the masses of the objects.

    • A has 6 times the mass of B.

    • B has 6 times the mass of A.

    • A and B have equal mass.

    • The situation as stated is impossible.

    Correct Answer
    A. B has 6 times the mass of A.
    Explanation
    Since weight is directly proportional to mass and the weight of object B on the Moon is the same as the weight of object A on Earth, we can conclude that the masses of the two objects are different. Since the Moon's gravity is one sixth of Earth's, object B must have a greater mass than object A in order to have the same weight. Therefore, B has 6 times the mass of A.

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  • 48. 

    A stone is thrown straight up. At the top of its path, the net force acting on it is

    • Greater than its weight.

    • Greater than zero, but less than its weight.

    • Instantaneously equal to zero.

    • Equal to its weight.

    Correct Answer
    A. Equal to its weight.
    Explanation
    When a stone is thrown straight up, at the top of its path, the net force acting on it is equal to its weight. This is because at the top of its path, the stone momentarily comes to a stop before it starts falling back down due to the force of gravity. At this point, the force of gravity pulling the stone downwards is equal in magnitude to the force exerted by the person throwing the stone upwards, resulting in a net force of zero. Since weight is the force of gravity acting on an object, the net force being equal to the weight means that the stone is in equilibrium at the top of its path.

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  • 49. 

    A horizontal force of 5.0 N accelerates a 4.0-kg mass, from rest, at a rate of 0.50 m/s^2 in the positive direction. What friction force acts on the mass?

    • 2.0 N

    • 3.0 N

    • 4.0 N

    • 5.0 N

    Correct Answer
    A. 3.0 N
    Explanation
    The friction force acting on the mass can be determined using Newton's second law, which states that force is equal to mass multiplied by acceleration. In this case, the force applied is 5.0 N and the mass is 4.0 kg, resulting in an acceleration of 0.50 m/s^2. By rearranging the formula, we can solve for the friction force. Therefore, the friction force acting on the mass is 3.0 N.

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